Much effort has been applied during the last twenty years or so in improvement of earth-burrowing devices. Development efforts have accelerated because of the high demand for equipment to bore underground passages without disturbing the ground surface (e.g., roadways). Some of the early work in this field included work by Bell Labs and Schramm Company's "Pneumagopher." More recently, innovations have been made by a number of companies.
Among the many U.S. Pat. Nos. relating to earth-burrowing moles are the following:
3,630,295 (Coyne et al.)
3,794,128 (Gagen et al.)
3,952,813 (Chepurnoi et al.)
4,026,371 (Takada et al.)
4,108,256 (Moore, III)
4,592,432 (Williams et al.)
4,596,292 (Crover)
4,621,698 (Pittard et al.)
4,632,191 (McDonald et al.)
4,646,277 (Bridges et al.)
4,662,457 (Bouplon)
4,694,913 (McDonald et al.)
4,708,211 (Shemyakin et al.)
4,787,463 (Geller et al.)
4,809,789 (MacFarlane)
4,834,193 (Leitko, Jr. et al.)
4,858,703 (Kinnan)
4,858,704 (McDonald et al.)
4,907,658 (Stangl et al.)
4,921,055 (Kayes)
4,928,775 (Lee)
4,938,297 (Schmidt)
4,958,689 (Lee)
5,002,137 (Dickinson et al.)
5,002,138 (Smet)
5,010,965 (Schmelzer)
5,031,706 (Spektor)
5,050,686 (Jenne)
5,056,608 (Hemmings).
The typical earth-burrowing mole has a missile-like elongate body which extends along an axis and a forward head designed for earth penetration. Inside the elongate body is a percussive drive means driven by pneumatic or hydraulic pressure which builds up and is released in a repetitive pounding action.
Existing earth-burrowing mole products have numerous problems, many of which relate to a lack of control of the direction of movement through the ground. Because of this, much of the development has related to controlling boring direction of the moles as they move underground, driven by pneumatic or hydraulic pressure which operates a percussion device. Typically, flexible pneumatic (or hydraulic) supply lines are connected to the rear of the mole and are dragged by the mole into the burrow as it is formed by the mole.
Systems which have directional control seek such control primarily by directing the forward movement of the mole off-axis by imposing slant-angled surfaces against the ground through which the mole moves. Such surfaces are typically a slant tip or fins. Efforts at obtaining directional control, however, have left many problems.
The Williams et al. patent discloses a boring unit with a pair of adjustable fins mounted near the front which serve to raise and lower the direction of underground travel. However, the Williams et al. device has only limited directional control. Furthermore, the Williams et al. device does not appear to be a mole in the normal sense, that is, a generally free-running device driven by fluids (pneumatic or hydraulic). Instead, it appears to be a device pushed by rigid pusher rods using a backhoe or the like. The Williams et al. device is not concerned with steering in the normal sense, that is, for severe course changes, but only with correction of the course of a pusher rod to an intended true horizontal direction.
Some of the patents disclose devices with adjustable fins which are located at the rear of the mole or other burrowing device. For example, the Gagen et al. patent steers by adjustment of fins to parallel planes. Stated more accurately, such patent discloses one adjustable fin which moves between a position for mole rotation and a mole-turning position parallel to the other fin.
The Gagen et al. device, with its rear fins, has considerable resistance to its attempts to change direction. This is because of the lateral resistance to turning along the length of the device. The devices of the Bridges et al. and Coyne et al. patents also have rear adjustable fins, and the same inherent disadvantage.
Among the recent developments has been a product sold by Allied under the commercial name "Guided Hole-Hog." The McDonald et al. '191 patent appears to be related to such product.
The McDonald et al. '191 patent relates to a device with a fixed-fin sleeve which is either free-wheeling or lockable and a beveled tip. As with certain other prior art devices, the beveled tip causes the mole to move off axis unless the elongate body is rotating about its axis; if it is rotated about its axis, the off-axis effect of the beveled tip is constantly experienced in different directions, which cancels out any tendency of the mole to change direction.
Such rotation of the elongate body is achieved by means of the rear fin arrangement which, when the fin sleeve is locked to the mole, causes the elongate body to rotate, thus keeping the mole on a generally straight course. On the other hand, when the fin sleeve is free-wheeling with respect to the remainder of the mole, the mole does not rotate and is driven off-axis by its tip. One embodiment in the patent is shown as having adjustable rear-mounted fins.
There are several disadvantages with the Guided Hole-Hog and other earth-burrowing moles of the prior art. Among these are the very long turning radius of mole turning, clearly insufficient turning forces which cause slow turning, the resulting inability to surface launch (as opposed to pit launch) the moles, the difficulty or impossibility of correcting a mole's direction of movement if it rotated too far, such that its beveled tip is beyond the intended turning direction, and the high cost of devices intended to solve some of the directional shortcomings.
Many earth-burrowing moles are on the market. Most either have no directional control systems or have control systems burdened with well-known disadvantages. Furthermore, to obtain a mole which has steerability of any sort typically requires a mole owner to discard his existing equipment and purchase a steerable unit.
In summary, there is a clear need for unique equipment overcoming the failings and disadvantages of the prior art. There is a clear need for an improved steerable mole for underground burrowing.